An actuating unit of this type is by way of example disclosed in the patent application DE 43 10 061 A1 of the applicant. A sensor arrangement that is merely illustrated in a simplified manner is used to ascertain the differential travel between the pedal connecting element and the brake boosting piston, said sensor arrangement being arranged in the region between the brake boosting piston and a pressure rod that is jointed in an articulating manner to the actuating pedal. As an example, a Hall sensor and also a permanent magnet can be used to achieve the sensor arrangement. Further disclosures regarding the construction of the previously known sensor arrangement are not evident in the disclosure of the mentioned publication. It thus remains inter alia open as to which path is to be used for the differential travel information to pass from the previously known sensor arrangement that is localized to the moving brake boosting piston to the electronic control unit that is fixed to the brake booster housing. A corresponding flexible electrical connection that does not impair the movement of the brake boosting piston is regarded as not being feasible with the necessary functional reliability.
The therefore initially obvious approach of separately ascertaining the two distances travelled by the pedal connecting element and the brake boosting piston relative to the brake booster housing using sensor arrangements that are fixed to the housing, said sensor arrangements forming and further processing the difference of the corresponding signals, is technically problematic because the differential travel that carries the essential information is approximately two orders of magnitude smaller than the two signals that are used. If by way of example the pedal connecting element travel signal comprises a deviation of +1% of its value range and the brake boosting piston travel signal comprises a deviation of −1% of its value range, this would cause an entirely unacceptable error of 200% of the differential travel signal. One consequence of this approach would be to lead to a comparatively complex and cost-intensive solution owing to the associated accuracy that is required for the two signals.
The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.